If you had no warning light then it suggests the fluid was still in spec from a viscosity standpoint.

Do you get a root cause failure analysis done that linked your transfer case failure with the fluid condition? If there were shards of metal, it sounds like something broke. That may or may not have been due to fluid condition. eg, if a bearing broke up, then I would see a connection. If a static part broke off and dropped into the works, or the actuator failed, not so much.

I don't think that changing the fluid as a preventative maintenance item is necessarily a bad idea. That presumes that the transfer case adaptations are reset in the computer, ie the fluid change is done correctly. I am just commenting on all the posts that suggest that doubling or tripling up on maintenance over what is recommended will necessarily result in longer component life.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue